CHECKING THE 120 VOLT AC STARTER MOTOR

CHECKING STARTER MOTOR DRIVE - TM-5-4240-501-14P_179

CHECKING THE RECTIFIER ASSEMBLY 120 VAC STARTER MOTOR

TM-5-4240-501-14P Special Diver Air Support System (SDASS) NSN 4220-01-292-3708 Manual
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TM 5-4240-501-14&P STARTERS Gear Drive 12V & 120V Insert the tachometer in the end of the starter motor shaft and activate the starter motor. A starter motor in good condition will be within the following specifications. 1. Starter motor RPM - 5,600 minimum. 2. Current - 6 amperes maximum (disregard surge current) CHECKING THE 120 VOLT AC STARTER MOTOR A performance test of the 120 volt starter motor may be made in the following manner. Equipment Needed - 1. A tachometer capable of reading 10,000 RPM. 2. An ammeter capable of reading 0 to 10 amperes AC (RMS). DANGER: The performance test of this starter requires the use of an ammeter, connected in the 120 volt AC starter motor circuit. Extreme care should be used in making this test to minimize the hazard of electrical shock. Clamp the starter motor in a vise as shown. An ammeter may be connected as shown in the accompanying illustration. Fig. 73. Plug the electrical cord into a 120 volt outlet and insert the tachometer in the end of the starter motor shaft. CAUTION: Starter motor housing contains two powerful ceramic magnets that may crack if motor housing is clamped in a vise or struck with a hammer or a hard object. Fig. 73 - Checking 120 Volt Starter Motoi Performance A starter motor in good condition will be within the following specifications. 1. Starter Motor RPM - 8,300 minimum. 2. Current -- 1/2 amperes maximum AC. If either the 120 volt AC or 12 volt DC starter motor does not perform satisfactorily, the following should be checked and corrected if necessary. 1. Binding condition between the pinion gear, helix and drive gear assembly. 2. Misalignment or binding between motor bearings. 3. Starter motor brushes sticking in brush holders. 4. Dirty or worn commutator. 5. Shorted, open or grounded armature. A. Shorted armature (wire insulation worn and wires touching one another) will be indicated by slow speed and high current. B. Open armature (wire broken) will be indicated by low or no RPM. C. Grounded armature (wire insulation worn and wire touching armature lamination or shaft) will be indicated by excessive current or no RPM. 6. A defective starter motor switch (in cord). 7. A defective starter motor rectifier assembly. 8. Weakened magnets. DISASSEMBLY OF STARTER MOTOR Study Fig. 69 prior to starter motor disassembly. NOTE: END HEAD, END CAP AND HOUSING MUST BE PLACED IN THE SAME POSITION AS WHEN REMOVED, OR INTERFERENCE MAY RESULT. See Fig. 74. Fig. 74 - Match Marks Remove thru bolts. Fig. 75. The end cap may then be removed. (See checking starter motor drive if repair, cleaning or replacement of drive assembly is necessary.) 20

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